The application proposes to develop an improved instrumentation for the derivation of EPR spectra from various EPR substrate probes that are to be implanted in or infused/suffused into living systems ranging from cells to animal models to humans, many of whom have in-dwelling EPR substrate probes in the form of Indian ink tattoos. Although there is no best frequency for such studies, the authors will focus on that frequency with which the laboratory has most extensive experience. New developments include 1: the development of an automatic matching circuit, and 2) the development of a magnetic field